Takashi Miyake

Electronic structure of C60-encapsulating semiconducting carbon nanotube

Abstract The electronic structure of a C60-encapsulating (14,7) carbon nanotube is studied by the local density approximation (LDA) in density-functional theory. The (14,7) nanotube is a semiconductor with the LDA gap of 0.5xa0eV. On the other hand, its fullerene-encapsulating form is a narrow-gap semiconductor with the LDA gap of only 0.2xa0eV. The top of the valence band has a nanotube-character, while the bottom of the conduction band is the C60 t1u band, because of descent of the C60-origin bands upon the encapsulation into the nanotube. Analysis of the charge distribution indicates that the descent of the C60 bands is due to hybridization with the nearly free-electron state of the nanotube.

Electronic properties of alkali-metal loaded zeolites: Supercrystal Mott insulators

First-principles band calculations are performed for an open-structured zeolite with guest atoms (potassium) introduced in the cages. A surprisingly simple band structure emerges which indicates that this system may be regarded as a ``supercrystal, where each cluster of guest atoms with diameter

GW study of half-metallic electronic structure of La0.7Sr0.3MnO3

ensuremath{sim}10mathrm{AA{}}

GW quasiparticle band structure of CaB6

acts as a ``superatom with well-defined s- and p-like orbitals, which in turn form tight-binding bands around the Fermi energy. The calculated Coulomb energy for these states turns out to be in the strongly correlated regime. We show, with the dynamical mean-field theory, that the system resides in the Mott-insulator regime in accord with experimental results. We envisage that this class of systems can provide a new avenue for materials design.

Quasiparticle Band Structure of Carbon Nanotubes

Abstract Half-metallic systems will be quite useful in future spin electronics. The GW approximation is employed to study electronic structure of half-metallic La0.7Sr0.3MnO3, to show that the lowest quasiparticle energy of the unoccupied minority spin states is far above the Fermi energy compared to that in the LSDA. As a bulk, this system is predicted to be a fully spin-polarized half-metallic ferromagnet.

Nanotube nanoscience : A molecular-dynamics study

Much controversy is aroused in the electronic structure of hexaborides both in theories and experiments. In order to settle this problem, the quasiparticle energies are calculated including the effects of electron correlations beyond the local density approximation in the stoichiometric calcium hexaborides. It is shown that electron correlation does not open the band gap, contrary to the naive expectation. This semimetallic band structure coincides with the magnetic oscillation measurements, and the origin of this abnormal quasiparticle shifts is elucidated as being closely connected with the details of the wavefunctions in the non-local interaction terms.

Quasiparticle band structure of carbon nanotubes

The electronic states of small‐diameter carbon nanotubes are investigated using the ab initio GW approximation. It is found that quasiparticle excitation energies are increased significantly in semiconducting nanotube due to the many‐body correction. Lifetimes of the quasiparticles are also calculated and turned out to be much longer in semiconducting tube than in metallic tube.